Forms of Forward Quadrupedal Locomotion I. A Comparison of Posture,
Hindlimb Kinematics, and Motor Patterns for Normal and Crouched Walking.
Trank, Tamara V., CheunJu Chen, and Judith L. Smith.
Laboratory of Neuromotor Control, Department of Physiological Science and
the Brain Research Institute, University of California, Los Angeles,
California, 90095-1568.APStracts 3:0132N, 1996.
SUMMARY AND CONCLUSIONS
1. Posture, hindlimb kinematics, and activity patterns of selected hindlimb
muscles were compared for normal and crouched treadmill walking (0.5-0.6 m/s)
for 8 cats. To elicit crouched walking in which the trunk and head were
lowered, cats were encouraged to walk under a light-weight Plexiglas ceiling
suspended 17-20 cm above the treadmill belt. Kinematic data were obtained from
high-speed cin[acute]e film, and electromyograms (EMGs)─synchronized with the
kinematic records─were taken from 11 hindlimb muscles. 2. The postures for the
two forms of walking were distinctly different. During crouched walking, each
cat lowered its entire body keeping its trunk horizontal to the treadmill
belt. Also the head was lowered, with the top of the head in line with the
dorsal surface of the trunk. Hip height, used as a measure for hindlimb
crouch, was reduced by 30%, from an average height of 23 cm to 16 cm above the
belt during the entire step cycle. 3. Average cycle periods (766 +/- 30 ms)
and percentage of time devoted to swing (30%) and stance (70%) were similar
for normal and crouched walking. The profiles of the hindlimb kinematics were
also similar for the hip, knee, ankle, and metatarsophalangeal (MTP) joints
during the step cycle, but the timing of some of the motion reversal, as well
as the ranges of motion during various phases, were different at some joints
for the two forms of walking. 4. During the swing phase, the transition
between the flexion and extension (F-E1 reversal) occurred later in the
normalized swing phase at the hip, knee, and ankle joints, and the range of
flexion was increased at each joint. With greater flexion at these joints, the
anatomical axis of the hindlimb (measured from hip joint to toe) was
decreased, and the hind paw advanced in the narrow space between the abdomen
and treadmill belt. At contact, the position of the paw was less anterior to
the perpendicular reference line (hip joint marker to belt) and all joints
were more flexed for crouched than normal walking. 5. Throughout the stance
phase, the knee and ankle joints remained significantly more flexed by 41-
45 during crouched than normal walking. Although the hip and MTP joints
started in a more flexed position at paw contact, both joints extended more
during stance for crouched than normal walking, and at the time of peak
extension (just before paw lift off), the degree of extension at the hip and
MTP joints was similar for both forms of walking. 6. Muscle patterns for
crouched and normal walking were similar with some exceptions. The burst
durations for three primary flexor muscles, the semitendinosus (ST; knee
flexor), extensor digitorum longus (EDL; ankle flexor), and flexor digitorum
longus (FDL; digit flexor) were longer for crouched than normal walking, and
this was consistent with the increased range and duration of flexion during
the swing phase of crouched walking. Also, two muscles that normally showed
mainly swing-related activity during normal walking, the EDL and the extensor
digitorum brevis (EDB), had distinct stance-related bursts that occurred after
midstance during crouched walking. 7. Crouched walking requires a postural
change that is typically seen when cats stalk prey and when cats walk up and
down steep slopes. Postural set during walking appears to be determined by
brain stem and diencephalic centers, and the postural orientation of the cat
may require adjustments in the motor program provided by spinal centers for
the cat to walk. The role of posture and locomotion and the adjustments in
hindlimb kinematics and EMG activity patterns have been studied for forward
and backward walking in the cat (Buford et al. 1990; Buford and Smith 1990;
Pratt et al. 1996; Trank and Smith 1996) and now for crouched walking on the
treadmill. These data will assist us in understanding the role of posture,
especially crouched posture, during other walking behaviors.

Received 6 March 1996; accepted in final form 4 June 1996.
APS Manuscript Number J180-6.
Article publication pending J. Neurophysiol.
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 28 June 96